So I have some worlds with different physics, and need some way to explain it. As with other sci-fi, it would seem best to find something plausible but may be extremely unlikely or have negligible effect, and then exaggerate it.

The universe has many layers of emergent properties. So the current approach is to have a tiny change in some physical constant* (or multiple) which results in a new emergent property in that world which isn't in other worlds, or an emergent property which does exist in other worlds not being in that world. To facilitate this, it was decided each world would be its own galaxy, that way they wouldn't interfere much with each other and we wouldn't need to possibly reinvent astrophysics, and each of those galaxies could have one or more planets with intelligent life** in there somewhere. The distance between galaxies is a lot more than the distance within, so it makes sense that these constants seem invariant within a galaxy but could differ significantly between them.

So then using this route, the question now is, how is it possible that different galaxies can have slightly different physical constants? Or alternatively, if we have no way to explain it, is there evidence of physical constants being inconsistent in our universe? If so, it could be reasoned this scifi universe is just copying our universe.

As for the curvature of the universe, it seems it depends on how much mass there is, since the mass curves it. So that's for the entire universe, and using my limited knowledge of relativity, I'd guess it applies locally as well, there's just not the mass (or lack of mass) to cause significant curvature. Which means, for example, a very small isolated galaxy would have low density locally, and thus have locally very slightly hyperbolic space. I'm not so interested in calculating this curvature since I'll exaggerate it anyway, but rather whether this would be possible.

*Not a constant anymore

**Let's just ignore for now how to get between these worlds and how life would be both similar enough and develop at around the same time to facilitate intergalactic relations.

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    $\begingroup$ "how is it possible that different galaxies can have slightly different physical constants?" - the simple answer is you can't because all galaxies in this universe are governed by the same rules. Our laws of physics don't apply to only our galaxy, they apply to our knowledge of the UNIVERSE, which includes EVERY GALAXY in said universe. $\endgroup$
    – Aify
    Commented Mar 1, 2018 at 22:09
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    $\begingroup$ inconsistent constants means your underlying theory is wrong. $\endgroup$ Commented Mar 1, 2018 at 22:36
  • $\begingroup$ Martin Rees, Just Six Numbers: The Deep Forces that Shape the Universe, 2001. (Link goes to Amazon.) $\endgroup$
    – AlexP
    Commented Mar 2, 2018 at 0:49
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    $\begingroup$ @a4android I think what he means is that the instant you find inconsistent constants, your theory is wrong, because your theory claims that that thing is constant, when it isn't. Physics people are prepared to create new theories which include a non-constant, if the evidence supports it. $\endgroup$
    – Cort Ammon
    Commented Mar 2, 2018 at 1:39
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    $\begingroup$ I'm loathe to make this an answer, but may I recommend using Sanderson's First Law of Magic here? Trying to pin macroscopic effects on tiny changes is an extremely difficult problem to solve without generating many inconsistencies. Your energy is typically best spent elsewhere unless you have a PhD in physics already. Bad physics in scifi stories is like using handwavium, except that you are also admitting that you're rather embarrassed about the handwavium. $\endgroup$
    – Cort Ammon
    Commented Mar 2, 2018 at 1:44

5 Answers 5


It is unlikely other galaxies have different physical laws or even slight variations in physical constants. The empirical evidence is against it. Measurements of light from different galaxies would betray the presence of variations in physical constants.

Of course, if evidence of variations, from light measurements, indicated there were variations in physical constants, then physicists would be revising their current theories faster than you can blink. Present indications are this is improbable and not likely to be happening anytime soon.

However, if you want to build a world, an alternative cosmos, where worlds exist with different physical laws, then one way to do this is to assume the existence of alternative universes where the physical laws are different. The next step is to assume that some of the worlds, these could be planets or even entire galaxies, have somehow slipped from their original alternative universes and are now located in our universe.

The assumption that there might be alternative universes with different physical laws is a scientifically reasonable concept. At the very least, our current understanding of nature doesn't prohibit their existence.


If we assume that World is a simulation (as many believe) it is fairly easy - each galaxy can be simulated by different cluster of servers with their own set of parameters.

Rolling out an update can propagate slowly (like DNS propagation) or it can be done only locally, to a particular set of server or clusters. If such update would contain altered physical constants different galaxies would end up with different physics.

  • $\begingroup$ This is a brilliant outside-the-box solution. Welcome to WorldBuilding.SE! I hope you stick around! $\endgroup$
    – F1Krazy
    Commented Mar 2, 2018 at 13:04
  • $\begingroup$ Thank you, this is the first idea that came to my head as I am looking for a novel that would expand upon this idea. I hope to stumble upon OP's book one day :) $\endgroup$ Commented Mar 5, 2018 at 8:31

Unfortunately, by definition of the term physical 'constants' can't really be different in different areas of the universe. If they could, I suppose they would be called physical variables instead. So, the only way this could happen is if you forget physical constants, and embrace physical variables.

In the real world, the gravitational constant is used to calculate the amount of gravity between to masses. This value never changes, so any two masses will always have the same gravitational pull between eachother. Always. Everywhere. No matter what. That's because a constant never changes. Observations of other stars, galaxies, and superclusters conform to how we expect gravity to behave, so we have no reason to believe it's not constant.

So, you must build your universe on the presumption that there are no physical constants. Although this goes against our current understanding and observations of the real universe, you're the one building this universe. Simply describe some mechanism for why physical properties can be locally constant(on a galactic scale), but cannot be properly predicted in distant regions of space. Maybe dark matter does some weird things, or some other as-of-yet unknown mechanism is manipulation our observations of the universe.

If the amount of space in space isn't constant, then there's probably weird other physical characteristics of our universe that we haven't yet observed. You certainly can come up with some handwavy-scientific reason that gravity or whatever else also isn't constant.

  • $\begingroup$ "Observations of other stars, galaxies, and superclusters conform to how we expect gravity to behave, so we have no reason to believe it's not constant." To be fair, there is this issue with dark matter, which is a tight fit because the gravity wasn't behaving as expected. The justifications for dark matter so far are "then everything works again" as I understand it. Or are there recent results where its existence could be proven directly, instead of indirectly as in "if it weren't there, these object should behave differently"? $\endgroup$
    – SK19
    Commented Mar 3, 2018 at 22:33
  • $\begingroup$ Reminds me of how the gravitational constant has a unit assigned just that the other units work in the formulas where it is used. $\endgroup$
    – SK19
    Commented Mar 3, 2018 at 22:35

I would go with dimensions, aka a multiverse

I once had an idea for a warp drive that not only moves you in space it actually moves you to another dimension. Most of the time, maybe the spin of an atom is different, but on rare occasions crew just cease to exist. In extreme cases, ships can be lost by jumping into dimensions with completely different physics. Of note is that in parallel dimensions your "other" would be on a similar ship making a similar jump, well at least most of the time, but perhaps not always :)

It makes for some interesting plot twists.

I won't be mad if you use it.


You describe the String Theory Landscape

I linked wikipedia on this to prove it is real but the article is tough going. Probably because the concepts involved are tough going. I did not get far on the Physics stack either though you can read about string theory landscapes there. My summary: the nature of our reality and its physical laws emerge from interactions of the 11 dimensional strings that comprise reality. A huge number (but not infinite) of different combinations are possible and each gives rise to a universe with different properties.

It is not clear to me if these different universes are actually thought to exist - a sort of multiverse - or if they are only theoretically possible.


Now, the KKLT model is but a very special case of a huge class of more general compactifications. One can imagine solutions where only four dimensions are compactified, or indeed where none of the dimensions are compactified and the universe exhibits the full eleven dimensions of M-theory. One could imagine that other fluxes are turned on, or that no fluxes are turned on. If we think of the string theory landscape as a huge potential or functional which varies depending on all of the different possible moduli, then it is clear that the quantum wilderness of string theory is a vast, higher dimensional cornucopia of moutaintops, valleys and precipices. The moduli space of supersymmetric vacua is rather like a vast plain extending up to the mountains - one may move continuously between different vacua by varying certain moduli. Accelerating cosmologies correspond to isolated valleys which sit up between the mountain peaks and passes (i.e., one might imagine equating the magnitude of the dark energy with the altitude of the valley). For whatever reason, we live in a universe where four spacetime dimensions are compactified, and our `altitude' is just barely above sea level.

Of course, when one starts to think of the universe in these terms, it can have a profound impact on one's expectations and outlook. It starts to look like many things - the masses of the elementary particles, the values of the couplings, the value of the cosmological constant - are probably just accidents, random numbers that will never be calculated from first principles using string theory.

For a world builder with an elementary knowledge of physics, this String Theory Landscape offers some sort of grounding in real theoretical physics which can justify different universes with different physical laws. I do not think you could go from one universe to another in a truck. I think these different universes would be more different realities than physically contiguous places.


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